Online measurement method of transformer leakage impedance by using symmetrical coupling auxiliary winding

The transformer can be illuminated by the T-type equivalent circuit model. The primary and secondary leakage impedance characterizes the copper losses and the exciting impedance reflects iron-core losses. The iron-core losses and the copper losses can be obtained by open-circuit and short-circuit test. However, the copper losses of the primary winding and the secondary winding cannot be separated, which cannot satisfy the requirement of the cooling design of the high power transformer. The auxiliary winding method to measure the winding ac resistance of planar transformer in high-frequency switching converters is used in Reference [1], but the detailed arrangement of the auxiliary winding is not analyzed. In this paper, an inductance-coupling model of the transformer is established, and the measurement error is analyzed. Then a Symmetrical Coupling Auxiliary Winding Measurement Method (SCAWM) is proposed. The measurement accuracy of the proposed method is verified by the experiment results based on a five-winding transformer. The online copper loss during nominal medium frequency operation condition is carried out based on the above method, which achieves the separating measurement of the primary and secondary winding AC resistance.